Apparatus for prilling



Aug. 19, 1969 M. H. TUTTLE 3,461,489

APPARATUS FOR PRILLING Filed March 4, 1966 5 Sheets-Sheet 1 INVENTOR.MALCOLM H. TUTTLE hll ATTORNEYS.

I M. H. TUTTLE APPARATUS FOR PRILLING Aug. 19, 1969 5 Sheets-Sheet 2Filed March 4, 1966 o 0 o o n 0 v :0 o 9 i: .1 It

FIGS

0 m T T N U E T v WH M L O M M mn'ronneys Aug. 19., 1969 H,-'TUTTL E3,461,489

APPARATUS 2 0R PRILLING Filed larch 4, 1966 1 5 Sheets-Sheet 3 FIG? I! EI 01 55 64 INVENTOR. MALCOLM H. TUTTLE BU L 1, M W1 W hi8 ATTORNEYS Aug.19, 1969 M. H. TUTTLE 3,461,489

APPARATUS FOR PRILLING Filed March 4. 1966 5 Sheets-Sheet 4 INVENTOR.MALCOLM H. TUTTLE B W s MI ATTORNEYS United States Patent 3,461,489APPARATUS FOR PRILLING Malcolm H. Tuttle, 56 Avon Road, New Rochelle,N.Y. 10804 Filed Mar. 4, 1966, Ser. No. 531,658

Int. Cl. B29c 23/00; B22d 23/08 U.S. Cl. 182.6 7 Claims ABSTRACT OF THEDISCLOSURE Prills are formed from molten material by expelling hot meltthrough sets of orifices drilled through the outer wall of a rotatingcentrifgual distribtuor on spaced horizontal planes and along lineswhich are related to the tangent, at the point of discharge, to thecircle described by the distribtuor as it rotates through angles whichdiffer in magnitude progressively from the upper to the lower portionsof the distribtuor so that jets of hot melt are discharged from thedistributor along sets of lines respectively slanted toward thedirection of rotation at the upper most plane of discharge and towardthe other direction at the next lower plane of discharge, and at relatedspeeds.

This invention relates to the formation of prills from molten materialand aims to provide an improved apparatus for prilling.

Prills are formed in a prilling tower, which is generally cylindrical inform, by expelling a molten material from a distributor through a seriesof holes to form drops of desired size. Those drops, which should beuniformly distributed across th area of the tower, fall through acurrent of air that cools and solidifies them and the solidified dropsare then collected at the bottom of the tower in the form of generallyspherical prills which are intended to pass through screens of specifiedmesh sizes.

In the past, two broad types of prilling apparatus have been used. Thefirst of these is known as the static shower-head type and the second isknown as the centrifugal bucket type. Neither of thee types of prillingapparatus has proved to be satisfactory in use:

The static shower-headed type of prilling apparatus would appear toafford separate control over drop size and distribution since drop sizewould seem to be governed by the size of the holes in the head and thepressure on the heads, while the size, number and location of headswould seem to govern distribution. However, in actual use, this has notbeen borne out and this type of installation has been beset by numerousproblems. The prills produced thereby vary widely in size and a largepercentage of broken prills is produced resulting in the creation ofdust, which is a loss, and a product which compacts and is hygroscopic.The major causes of the big variation in the size of the prills producedthrough the static shower-head type of prilling apparatus are (1) dirtyshower heads, (2) collisions between drops from adjacent heads, and (3)the impossibility of maintaining uniform melt pressure in all heads.

(1) Dirty shower heads result from the accumulation of foreign matterbecause of the difficulty of determining, during operation, which holesare obstructed. It is also difficult to remove and replace a shower headwhich is in operation.

(2) Collisions between drops often cause drops to coalesce to form dropsof such size that solidification is not completed before the dropsstrike the bottom of the tower and break by impact, causing coagulationof good prills and a build-up on the bottom. Collisions between dropsalso cause splatter and the formation of undersized prills and dust.Higher towers have been used in an at- "ice tempt to cool the oversizeprills but this also increases breakage of solidifield prills because ofhigher impact. De-dusting equipment has been installed to eliminate dustfrom the product. These attempted solutions have added to the cost ofthe equipment and to the operation and have not solved the problem ofthe formation of dust and off-sized prills.

(3) The desirable feature of uniform distribution is approached with theshower head type spray by providing numerous heads spaced so as to givea good distribution pattern. This requires manifolding of the heads insuch as way as to maintain equal pressure in the heads. When there is adifference or variation in pressure, both the size ad spread(distribution) of the drops are affected. In actual plant operation,lack of uniform pressure is a common cause of over and undersized prillproduction.

Since specifications normally control the size of marketable prills,prills not meeting the specification can only by recovered by remeltingand recycling. This not only adds to the cost of operation but oftenresults in an inferior product.

The inability of the static shower head type of prilling apparatus toprovide independent control of size and distribution of the dropsdelivered thereby has resulted in the general adoption of a centrifugalbucket type of prilling apparatus wherein prill size has been effectedby factors which control distribution. In this centrifugal type ofapparatus, as used in the past, the distributor is bucket-shaped and isrotated by a central shaft attached to the bottom of the bucket. Holesare drilled in the side wall of the bucket and melt added to the bucketis discharged radially by centrifugal force. As jets of melt leave theholes, the velocity of a jet with respect to the tower is the resultantof the velocity of the jet with respect to the bucket and the velocityof the periphery of the bucket with respect to the tower. When thediameter of a bucket is made the same at the top and the bottom, theperipheral velocity of holes at the top and bottom would be the samebut, on account of the difference in height, the centrifugal force atthe bottom would be greater than the force at the top so the velocity ofthe jets leaving the holes would be greater at the bottom than at thetop, causing a longer travel from the bottom than from the top. Thiswould result not only in bad distribution but upper streams of meltwould cross the paths of lower streams and cause collisions to produceoffsize prills. To avoid acrossthe stream flow, it was customary to makethe bottom of the bucket with a smaller diameter than the diameter ofthe top. When the difierence in diameters caused a slope of the bucketside to exceed about 11 degrees, melt would wet the outside of thebucket and by centrifugal force travel up the outside to the top edgewhere it would be thrown off as a mist, or, with greater angles, as asheet, to form dust and particles not suitable for the finished product.

A very serious disadvantage of the sloping sided bucket as used in thepast is that drops are formed under one set of conditions of peripheraland centrifugal forces at the top and widely different conditions at thebottom. It is known that high peripheral velocities tend to producesmaller sized drops but with peripheral velocities above about 15 feetper second, an increase in the hole size tends to cause the jet to breakinto drops of all sizes. High peripheral velocities are required at thetop of the conventional sloping sided bucket in order to distributeprills to the walls of the prilling tower but low velocities are neededto distribute prills toward the center of the tower. Bcause of thelimitation on the useful slope of the bucket, it was not possible todistribute over an area greater than about 70% of the tower area, andthis required employment of velocities which cause wide variation inprill size.

I have discovered that is possible to overcome the disadvantages,referred to above, that have been inherent in the use of the staticshower head typeof prilling apparatus and in the past centrifugal buckettype of prilling apparatus by means of a distributor mounted forrotation about a perpendicular axis and having a side wall provided withrows of holes through which the melt may be expelled through centrifugalforce in jets, the disposltion of the holes in the distributor wallbeing such that the angles at which the expelled jets of melt leave therotating distributor are so adjusted as to cause those jets to travel atdifferent but related velocities with respect to the prilling tower:

I have found that, when melt is discharged from a rotating centrifugaldistributor, advantage can be taken of the fact that the force withwhich it is discharged and the distance of its horizontal travel in theprilling tower are dependent upon the resultant of its combined jet andperipheral velocities; and this resultant velocity is, in turn, afunction of the direction in which the melt is discharged from therotating distributor. When a jet of melt is discharged from aconventional bucket-type distributor, the angle formed by the line alongwhich it emerges and the tangent, at the point of emergence, to thecircle described by the wall of the bucket as it rotates (which I shallrefer to herein as the angle of discharge) is a right angle. When thejet is discharged along a line that is directed toward the direction ofrotation of the distributor, so that the size of the angle of dischargeis decreased, the resultant velocity of the jet is correspondinglyincreased. Conversely, when the jet is discharged along a line that isdirected away from the direction of rotation of the distributor, so thatthe size of the angle of discharge is increased, the resultant velocityof the jet is correspondingly decreased. Accordingly, in the practice ofmy invention, the drops that are to be solidified into prills are formedby expelling the melt through holes extending through the wall of acentrifugal distributor along lines located at spaced horizontal planesand the sets of drops expelled from the holes along the respectiveplanes are distributed over related sets of adjacent concentric annularareas by progressively decreasing the travel velocities of therespective sets, through variations in the magnitudes of the angles ofdischarge of the melt from the distributor, from a minimum for the setof drops from the highest plane to a maximum for the set of drops fromthe lowest plane. As a consequence, the prills that I produce are ofmore uniform size than those that have been made in the past, build-upin the prilling tower is reduced, and, during their formation, my prillsare uniformly distributed over the total cross-sectional area of theprilling tower.

The apparatus that I have invented for use in the practice of myinvention includes a cylindrical tower, a perpendicular distributormounted for rotation adjacent the top of the tower, and means fordelivering melt to the distributor, for rotating the distributor and forcausing a current of air to flow upwardly through the tower. Thedistributor has a side wall which includes an arcuate area that isdefined by the surface of a segment of a cylinder whose radius isshorter than the distance from the axis of the tower to the wall of thedistributor. That arcuate section is provided with a row of holes thatextend through the wall along radii which are intersected by a pathconnecting a point near the lower trailing edge of the arcuate area anda point near its upper leading edge.

The apparatus that I have invented for use in the practice of myinvention, in the form that I now prefer, is illustrateddiagrammatically in the accompanying drawing in which:

FIG. 1 is a vertical section of prilling apparatus embodying myinvention;

FIG. 2 is a plan view, on an enlarged scale, along the lines 22 of FIG.1;

FIG. 3 is a vertical section, on an enlarged scale, of the centrifugaldistributor illustrated in FIG. 1;

FIG. 4 is a fragmentary view along the lines 44 of FIG. 3;

FIG. 5 is a fragmentary view along the lines 55 of FIG. 3;

FIG. 6 is a vertical section illustrating a modification of thedistributor illustrated in FIG. 3;

FIG. 7 is an enlarged front elevation of a modified form of arcuatesection of the type included in distributors illustrated in FIGS. 3, 5and 6;

FIG. 8 is an elevation, broken away in part, of a modified type ofdistributor;

FIG. 9 is a vertical section of a further modification of a distributorembodying my invention;

FIG. 10 is an elevation, broken away in part, of an adjustabledistributor head embodying my invention;

FIG. 11 is a section along the lines 1111 of FIG. 10;

FIG. 12 is an elevation, broken away in part, of a further modificationof an adjustable distributor head embodying my invention;

FIG. 13 is a section along the lines 1212 of FIG. 12; and

FIG. 14 is an elevation of one of the distributing elements in themodification illustrated in FIG. 12.

The prilling apparatus illustrated in FIG. 1 includes a cylindricaltower 20 having a prill collector at its lower end which includes: ascraper 21 mounted for rotary movement and adapted to scrape prillsfalling on the floor 21a through an opening 21b to a horizontal conveyor210. A centrifugal distributor 22 is suspended on shaft 23 adjacent theupper end of tower 20 and is rotated with shaft 23 by means of motor 24.Passages 26 admit air to tower 20 adjacent its lower end and air isexhausted from tower 20 through passages 27 by means of blowers 28.

The centrifugal distributor 22 illustrated in FIGS. 1-5 is in the formof a bucket and includes a bottom plate 30, which supports a corrugatedgenerally cylindrical side wall 31 having semicircular ridges 32 andcorrugations 33 and a top plate 34, having opening 35 therein, is fixedto side wall 31. An axial tube 37, which supports feed tube 38, extendsthrough opening 35 and is fixed to the bottom plate 30 so that it maysurround shaft 23. A conduit 39 connects the melt hopper 40 with theinterior of feed tube 38. The shaft 23 has a key 41 pivotably mounted inthe slot 42 at its lower end by means of pin 43. The key 41 is adaptedto fit in keyway 44 in the bottom of plate 30 to support distributor 22and to rotate that distributor with shaft 23. The distributor 22 can beremoved from shaft 23 by raising it to a point where the key 41 can bepivoted to a position in which it is parallel with shaft 23 and thedistributor may then be permitted to drop off the shaft. Vanes 45 arefixed to the inner surface of wall 31 for the purpose of causing meltfed to the interior of distributor 22 to rotate therewith and at thesame speed.

An upper hole 46, a lower hole 47 and intermediate holes 48 are formedin each of the semicircular ridges 32. These holes are disposed along apath which connects hole 48, located at the lower trailing edge of itsridge 32 when the distributor 22 is rotated, with hole 46, located atthe upper leading edge of its ridge 32 when distributor 22 is rotated.Each of holes, 46, 47 and 48 extends through the portion of the wallforming its semlcircular ridge 32 along a radius of that ridge.

The centrifugal distributor 22 illustrated in FIG. 6 18 also in the formof a bucket. The bottom plate 30 supports corrugated side wall 31'which, for purposes that Will be described hereinafter, tapers inwardlyfromits top to its bottom and has semicircular ridges 31' andcorrugations 33. A top plate 34 having an opening 35' therein is mountedon side wall 31'. Axial tube 37, which supports feed tube 38', extendsthrough opening 35' and is fixed to the bottom plate 30' so that it maysurround shaft 23. Conduit 39' connects a melt hopper with the interiorof feed tube 38. Shaft 23 has a key 41' pivotally mounted in slot 42 atits lower end by means of pin 43'. The key 41' is adapted to fit inkeyway 44' to support and rotate distributor 22 with shaft 23'. Vanes 45are fixed to the inner surface of wall 31 to cause melt in distributor22' to rotate with, and at the same speed as, distributor 22'.

Each of the semicircular ridges 32' has a series of radial holesincluding upper hole 46, lower hole 47' and intermediate holes 48 whichare disposed along a path connecting those holes. Hole 47 is located atthe lower trailing edge of ridge 32 when distributor 22 is rotated,while hole 46 is located at the upper leading edge of that ridge and theintermediate holes 48' occupy intermediate positions along that ridge.

The ridges 32 of centrifugal distributor 22 (and the ridges 32 ofcentrifugal distributor 22) can be replaced by ridges 49 of the typeillustrated in FIG. 7 which contain, in addition to the row of angularlyrelated radial holes 50, subsidiary rows of radial holes 51 and 52 thatare also angularly related to each other, when it is desired to increasethe number of holes of a given diameter that are employed beyond thenumber that may be accommodated in a single row.

A rotating arm type of centrifugal distributor is illustrated in FIG. 8wherein tubes 55' are mounted on hollow arm 56 so that the axes of tubes55 are vertical and parallel to the axis of hollow shaft 57 which isrotated by variable speed motor 58. Shaft 57 is supported and guided bystufling box bearings 58 which form the ends of a housing 59. A conduit60' connects a melt feed hopper 61, which is provided with a suitableheating element (not shown) with housing 59. Between stuffing boxbearings 58 and within housing 59 the hollow shaft 57 is drilledradially to provide passageways 63 from housing 59 to the interior ofshaft 57. A series of horizontally spaced radial holes 64 is drilled ineach of tubes 55 and those holes are positioned with respect to thedirection of rotation of shaft 57 to provide the angles of discharge forthe melt that will insure uniform distribution of the drops of meltexpelled through holes 64.

A modified rotating arm type of centrifugal distributor that may beemployed for the prilling of heat-sensitive substances where it isdesirable to hold the melt at high temperature for the shortest possibletime is illustrated in FIG. 9. It includes a series of tubes 70connected, through hollow arms 71, with box 72 which is constructed of abottom plate 73, a generally cylindrical side wall 74 and a top plate75. The box 72 is suspended from drive shaft 76 to rotate therewith bymeans of key 77 pivoted to that shaft at 78 and adapted to occupy thekeyway 79 in bottom plate 73. An axial tube 80, which surrounds shaft76, is fixed to bottom plate 73 and supports feed tube 81. A conduit 82which communicates with the interior of feed tube 81, leads to a meltfeed hopper (not shown). Vanes 83 are provided in box 72 to cause meltfed to the interior of that box to rotate therewith and at the samespeed. Each of tubes 70 is provided with radial holes 84 through whichthe melt is expelled. Those holes are positioned with respect to thedirection of rotation of shaft 76 to provide the angles of discharge forthe melt that will insure the desired uniform drop distribution of themelt expelled through them.

In the rotating arm type of centrifugal distributor, the vertical tubesfrom which the melt is discharged can be constructed so that the anglesof discharge can be changed. This may be accomplished by substitutingfor the continuous tubes 55 illustrated in FIG. 8 (or the continuoustubes 70 illustrated in FIG. 9) a demountable tube such as thatillustrated in FIGS. -11, or a composite tube such as that illustratedin FIGS. 12-14.

The tube 90 illustrated in FIGS. 10 and 11 consists of a cylinder 91having a row of angularly related radial holes 92. The cylinder 91 ismounted on a boss 93 carried by hollow arm 94 so that it can beadjustably rotated on that boss. The cylinder 91 is provided with a cappiece 94 that is engaged by washer 95. A bolt 96, whose head 97 engagesthe bottom of boss 93, extends upward through the cylinder 91 and thecap piece 94 along the axis of tube 90. A nut 98 on the threaded upperend of bolt 96 can be tightened to lock cylinder 91 into the position onboss 93 where the disposition of holes 92, with respect to the directionof rotation of the centrifugal distributor equipped with tube 90, isbest adapted to provide the angles of discharge for melt expelledthrough those holes that will insure the desired uniform dropdistribution of that melt.

The composite tube 100 illustrated in FIGS. 12-14 is made of a series ofmating annuli 101 adapted to be nested together is illustrated in FIG.12. Each annulus 101 is provided with a radial hole 102. A stack ofnested annuli 101 is mounted on boss 103 which is fixed on the end ofhollow arm 104 and the tube formed thereby is closed at its upper end bycap piece 105. The stack of annuli 101 is assembled so that therespective radial holes 102 are in the positions, with respect to thedirection of rotation of the centrifugal distributor equipped with arm104, that are best adapted to provide the angles of discharge for meltexpelled through them that will insure the desired uniform dropdistribution of that melt. The annuli 101 and their cap piece 105 arelocked in assembled position by means of bolt 106 whose head 107 engagesthe lower face of boss 103 and whose upper end is threaded to receivenut 108 that forces washer 109 against the top of cap piece 105.

The operation of the apparatus which I have invented will now bedescribed and, in connection therewith, it should be noted that detailsin the design of the apparatus employed will vary with variations inoperating conditions. For instance, the size, number and dispositions ofthe exit holes in my centrifugal distributor will be governed by factorssuch as the qualities of the melt being processed, the size of theprills to be produced therefrom, the rate at which the prilling is to becarried out and the dimensions of the prilling tower. Hence, the jet andperipheral velocities and hole diameter which are best suited for thesize prill to be produced are first established. Having established saidvalues, and referring to apparatus of the type illustrated in FIGS. 1-5by way of example, the shaft 23 is brought to the desired rotationalspeed by motor 24. Melt is fed from hopper 40 to the interior of feedtube 38 through conduit 39 and it flows to the bottom of distributor 22where it contacts bottom plate 30 and vanes 45 which bring the melt upto the rotational speed of the distributor. Under the effect ofcentrifugal force the melt rises along the inner surface of the wall 31to cover the exit holes 47, 48 and 46 through which the melt is discharged at a velocity dependent upon the rotational speed of thedistributor and the thickness of the melt layer therein.

When the jet velocity from the bottom holes 47 is made equal to theperipheral velocity and is directed in an opposite direction to thedirection of rotation, the resultant velocity with respect to the toweris zero and the jet breaks into drops which fall to the center of thecollecting surface of the tower. The centrifugal force acting on theupper holes 46 is not quite as great as the centrifugal force at thebottom holes 47 but as the upper holes 46 face in direction of rotation,so that they have a smaller angle of discharge, the resultant velocity,which is the sum of the peripheral and jet velocities, causes ahorizontal travel of these drops, while falling, across the full radiusof the tower. It may not be necessary to face the top holes completelyin the direction of rotation to cause sufficient travel to reach thetower wall. To prevent impingement on the wall without reducing jet orperipheral velocities, the top holes 46 may, in some cases, be turnedoutward or even slightly backward to give a resultant horizontalvelocity sufficient to cause prills to move to the outer edge of thecollecting area. The drops from the intermediate holes 48 travel throughhorizontal distances ranging from the minimum for the drops from holes47 to the maximum for the drops from holes 46. As the drops fall to thebottom of tower 20, they are cooled and solidified into spherical prillsby a current of air admitted to the interior of tower 20 through inlets26, and exhausted therefrom by blowers 28.

The modifications of my new prilling apparatus that are illustrated inFIG. 6, FIG. 8 and FIG. 9, respectively, operate upon similarprinciples. But, as one of these configurations may meet a special setof operating conditions better than the others, the particularconfiguration to be chosen for a particular use should be governed bythe conditions encountered therein. For instance, the distributor havinga vertical side wall of the type illustrated in FIGS. 1-5 has proved tobe superior Where it may be operated constantly at or near designconditions. However, where the operation is subject to changes in feedrate at frequent and short intervals, a distributor with a tapered sidesuch as that illustrated in FIG. 6 is preferred. This is illustrated bythe results produced through comparable runs in the prilling of urea:

(l) A distributor of the type illustrated in FIGS. 15, wherein the sidewall had a uniform diameter of ten inches and a height of ten inches,distributed prills over 99% of the cross-sectional area of a prillingtower forty-four feet in diameter when operated at 400 rpm. and with afeed rate of 220 tons of molten urea per day. However, when the feedrate was reduced to 134 tons per day (61% of design rate), the prillswere distributed over only about 58% of the tower area, resulting in anincrease in the weight of prills deposited per square foot of areacovered.

(2) Under similar conditions, a tapered distributor of the typeillustrated in FIG. 6, having an upper diameter of ten inches, a lowerdiameter of nine inches and a height of ten inches, when operated at 400rpm, distributed prills over 98% of the tower area at a feed rate of 220tons of molten urea per day, whereas, when the feed rate was reduced to134 tons per day, the area covered by prills was 60% of the tower area,the weight of prills deposited per square foot of area covered wasapproximately the same as the rate of 220 tons per day, and cooling wasnot impaired. With a further increase in the taper of this distributor,obtained by reducing the lower diameter to eight inches, the tower areascovered were: (a) at the rate of 220 tons per day, 97%; and (b) at therate of 132 tons per day (68% of design rate), 67%, resulting in areduction in the prills deposited per square foot of covered areas asthe feed rate is reduced; and cooling was improved over operation at thedesign rate.

In each of these runs, the results were superior by far to the resultsproduced in comparable runs wherein the best available prior artdistributor was operated under like conditions.

The terms that I have used in describing the illustrative embodiment ofmy invention that is illtgtrated in the accompanying drawing are termsof description and not of limitation. It will be appreciated thatchanges can be made in the preferred embodiment of my invention that Ihave described without departing from the spirit of my invention as itis defined in the appended claims.

What I claim is:

1. Prilling apparatus comprising:

a cylindrical tower;

a perpendicular centrifugal distributor mounted adjacent the top of saidtower for rotation about its axis said distributor having a side wallincluding an arcuate area, defined by the surface of a segment of acylinder whose radius is shorter than the distance from said axis tosaid wall, that is provided with a row of holes extending through thewall along radii which are intersected by a path that connects a pointadjacent the lower trailing edge of said area with a point adjacent theupper leading edge of said area;

means for delivering a molten substance to said distributor at its upperend;

means for rotating said distributor; and

means for causing a current of air to flow upwardly through said tower.

2. Prilling apparatus according to claim 1 wherein said distributor is abucket having a corrugated side wall provided with a series of verticalridges, each of which constitute an arcuate area provided with a row ofholes.

3. Prilling apparatus according to claim 2 wherein said bucket has avertical side wall.

4. Prilling apparatus according to claim 3 wherein said bucket has aside wall tapering inwardly from top to bottom.

5. Prilling apparatus according to claim 1 wherein said distributorincludes a series of hollow arms supporting and communicatingrespectively with the interiors of a series of vertical cylindricaltubes, each of which provides an arcuate area having a row of holes.

6. Prilling apparatus according to claim 5 wherein each of said verticaltubes is mounted for adjustable rotary movement with respect to its arm.

7. Prilling apparatus according to claim 5 wherein each of saidcylindrical tubes is formed from a vertical series of adjustablymounted, nested elements, each having a radial hole extending throughits wall.

References Cited UNITED STATES PATENTS Re. 12,568 11/1906 Cowing 18-262,571,069 10/1951 Shearman l82.6 3,055,049 9/1962 Bruyne et al. 18-2.63,285,722 11/1966 Levecque et al. 182.5 XR

WILLIAM J. STEPHENSON, Primary Examiner

